ADP-ribose polymers were isolated from living mammalian cells, separated by polyacrylamide gel electrophoresis, visualized in the gel with a novel silver staining agent, and quantified by computer-aided scanning densitometry. This method detects as little as approximately 40 fmol of ADP-ribose polymers of a particular size class and reduces the gel exposure times required for conventionally radiolabeled polymers from 2 months to about 1 h. The method also detects polymers with slow turnover which may be underestimated by techniques requiring metabolic radiolabeling of poly(ADP-ribose).